两侧对称动物在寒武纪繁衍旺盛，因此追踪它们的起源对了解动物是如何进化而来的十分重要。
Bilateral animals flourished in the Cambrian so tracing their origins is crucial to understanding the pace of animal evolution.
状况变得很清楚：只有真实的化石，才能为两侧对称动物出现的时间提供确凿的证据。
It had become clear that only actual fossils would furnish incontrovertible evidence for the time at which bilaterians had emerged.
在前一种中，左右型对称骨片的存在证实该动物两侧对称。
Left right sclerite pairs are found which proves a bilaterally symmetrical body of the animal.
脊索动物两侧对称、三胚层，分节的体腔，在胚胎发育的早期过程中，显示为后口类型。
Chordates are bilaterally symmetrical, triploblastic, segmented coelomates which demonstrate a deuterostomic pattern of early embryonic development.
脊索动物两侧对称、三胚层，分节的体腔，在胚胎发育的早期过程中，显示为后口类型。
Chordates are bilaterally symmetrical, triploblastic, segmented coelomates which demonstrate a deuterostomic pattern of early embryonic development.
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